Grinding or sharpening through the use of belt grinders whereby a contact wheel is powered to drive an endless abrasive belt which is riding over an idler pulley is well known in the art. Customarily such grinding was accomplished by bringing the entire forward facing surface of the work piece to be ground flat against the abrasive belt where it is backed by the contact wheel. Recently, however, one edge of a contact wheel has been relieved on a radius, and an endless belt positioned to extend out over this relieved radius and beyond the outer edge of the contact wheel. Work pushed against this abrasive belt and contact wheel results in grinding pressure being exerted, not only on the portion of the work piece in contact with the cylindrically supported portion of the abrasive belt, but also on that portion extending out beyond the wheel. The pressure varies from full pressure over the belt backed by the contact wheel to the point where the belt parts contact with the work. The only pressure beyond the contact wheel is that occasioned by the centrifugal action of the abrasive belt itself. The result achieved is a smooth, even taper from the point of full backup contact by the wheel to the point where the abrasive belt is no longer in contact with the work piece.
The same result can be achieved with the use of a dressed carbide cutting wheel, but the exact shape of the carbide wheel at any particular point in time is directly related to its original shape and the amount of work piece material which has previously been removed by the wheel. The wheel is abraded away each time it is brought in contact with a work piece, and so its shape is constantly changing. To pressure balance in the rotary blade work piece, therefore, it is necessary that each end of the grinding blade be sharpened in consecutive order on the same carbide cutter wheel. In other words, the blade has to be sharpened on one end, and then reversed end for end and sharpened on the other end to insure that the only difference in the shape of the carbide cutter from the beginning of the first sharpening to the end of the second sharpening is occasioned by the wear on the cutter during those two sharpening operations.
Since the very process of cutting causes the carbide cutter wheel to be abraded away, it is not precisely the shape to which it is dressed after it first removes its first material on the first cut after it has been dressed. Thus many interruptions of the grinding process are necessary so that the carbide cutter can be redressed to the proper shape.
Also, each time the wheel is so dressed, the working diameter of the wheel is reduced, so the jigs holding the work pieces to be ground by the carbide cutters cannot continuously hold the blades for an accurate cut, and must somehow be modified to take this change in outer diameter of the cutter into consideration.
Working with carbide cutters in the manner set out above, one man can sharpen a maximum of about 1,800 blades per day at a processing cost of about 6 cents per blade.
Needed to overcome the difficulties with the prior art methods was an apparatus whereby precisely identical cuts can be made at each end of work piece rotary blades, time after time after time, so that the blades will not have to be turned end for end and exposed to sharpening by the same grinding means at each end of the blade.